Intraocular stray light and multifocal soft contact lenses fit with a myopia control approach

Abstract

Objectives:

Center-distance multifocal contact lenses (MFCLs) are used to slow myopia progression. We examined the effect of two MFCLs on intraocular stray light values in myopic individuals.

Methods:

Twenty-five young myopic adults were enrolled and were fit with three contact lenses (Biofinity sphere, Biofinity Multifocal, NaturalVue Multifocal) in random order over two study visits. Pupil size (Neuroptics VIP-300, Laguna Hills, CA) and contact lens centration were measured. Right eye intraocular stray light measurements were collected (OCULUS C-Quant; Wetzlar, Germany) and compared to a spectacle trial lens. Log Straylight (LogSL) values and straylight residuals were analyzed using repeated-measures ANOVA with Tukey’s-corrected post-hoc t-tests.

Results:

Mean participant age (± SD) was 24.1 ± 1.5 years and right eye spherical equivalent refractive error was −3.38 ± 1.53 DS. There was no difference in mesopic pupil size between visits (p = 0.68) and no difference in contact lens centration between lenses (p = 0.99). LogSL values differed by lens type (p = 0.004). LogSL with the spectacle trial lens was significantly greater than with each contact lens type (all p < 0.05), but there were no significant differences in LogSL between the three contact lenses (all p > 0.05). There was no difference between the three contact lens designs for straylight residuals (p = 0.33)

Conclusions:

Measured intraocular stray light for both MFCLs was not different than with a spherical soft contact lens. A significant increase in intraocular stray light with spectacle trial lens correction was observed compared to all contact lenses.

Introduction

Methods to slow the progression of myopia have been of significant interest to the eye care community for many years, resulting in various treatment approaches.^1–3 Multifocal soft contact lenses have become a popular option for eye care practitioners due to their ease of adaptation and safety profile.^4–10 Soft contact lens approaches to myopia control have relied on the application of myopic defocus to the retina while providing clear foveal vision, and off-label usage of center-distance multifocal soft contact lenses designed for presbyopia correction have been used to achieve this goal.^11–16 Soft multifocal contact lens designs that add bifocal power in the periphery of the contact lens (center-distance) operate through the principal of simultaneous vision¹⁷ and have been used to provide acceptable high contrast vision while inducing myopic defocus.^{18, 19} More recently, other soft contact lens designs have also been utilized, such as extended depth of focus designs for presbyopia and dual focus contact lenses.^{10, 20–23}

While soft contact lens methods used to slow the progression of myopia have been shown to provide good high contrast visual acuity, they reduce low-contrast acuity, reduce contrast sensitivity, increase halos, and cause subjective visual disturbances.^24–26 One potential contributing factor the observed changes in visual quality may be an increase in intraocular straylight with use of multifocal contact lens optics. Intraocular straylight has been shown to have a significant effect on visual performance²⁷, and straylight-associated symptoms are similar to those reported with multifocal contact lens use such as hazy vision, decreased contrast sensitivity and disability glare.^{17, 28, 29} Intraocular straylight levels do not need to be extreme to affect vision, and low levels of intraocular straylight have been shown to significantly increase halo size and reduce contrast sensitivity.²⁷

Previous work examining intraocular straylight with multifocal optics did not examined multifocal contact lenses fit as used to control myopic progression.³⁰ With increasing adoption of myopia control in clinical practice, clinicians need to understand the potential visual effects multifocal contact lenses may have on non-presbyopic patients. The goal of this study was to examine the intraocular straylight encountered with a center-distance multifocal contact lens and an extended depth of focus design fit with a myopia control approach, compared to standard single vision corrections.

Methods

This study was conducted in accordance with the tenets of the Declaration of Helsinki and was approved by the Institutional Review Board of the University of Houston. Written informed consent was obtained from all participants and the study was registered on ClinicalTrials.gov (NCT03705130).

Overview

This was a two visit, single-masked, non-dispensing study that examined twenty-five adult myopic participants, aged 21 to 29 years old. Participants were excluded if they had any of the following conditions that could affect the optics of the cornea and crystalline lens: 1) history of ocular trauma, 2) significant anterior segment disease, including corneal dystrophies, 3) corneal or crystalline lens opacity that reduced best corrected visual acuity, 5) previous corneal or refractive surgery, or 6) current use of rigid gas permeable contact lens. Eligible participant had spherical equivalent refractive error between −0.75 DS and −6.00 DS at the corneal plane, refractive astigmatism of −1.00 DC or less at the corneal plane, and best corrected visual acuity of at least 20/30 in each eye. Individuals who reported being pregnant or nursing were excluded. Participants reported to each study visit wearing their habitual spectacle correction to avoid the potential of corneal staining induced straylight scatter.³¹

Eligible participants were fitted with three different contact lens designs. Two of the contact lenses feature center-distance optics that have been investigated for the ability to control myopia progression, the Biofinity Multifocal “D” +2.50 add (CooperVision, San Ramon, CA) and the NaturalVue Multifocal (Visioneering Technologies, Alpharetta, GA).^{16, 21, 22, 32} The Biofinity Multifocal “D” is a progressive aspheric design with a central spherical power for distance correction surrounded by a progressive zone of increasing plus power. The NaturalVue Multifocal is an Extended Depth of Focus (EDOF) design with a rapid increase in plus power near the center of the lens followed by a return to distance power outside of the plus zone and is indicated for use in presbyopic patients requiring up to a +3.00D add.³³ The third contact lens design is a single-vision contact lens, the Biofinity sphere (CooperVision, San Ramon, CA), used as control. Contact lenses were fit in random order, based on a computer-generated randomization schedule. Table 1 summarizes the contact lens parameters.

Table 1.

Comparison of contact lens parameters and optical designs.

Lens Name	Material	Water Content	Base Curve	Overall Diameter	Add Power
Biofinity Sphere	comfilcon A	48%	8.6mm	14.0mm	N/A
Biofinity Multifocal	comfilcon A	48%	8.6mm	14.0mm	+2.50 Center-Distance Progressive Asphere
NaturalVue Multifocal	etafilcon A	58%	8.3mm	14.5mm	Extended Depth of Focus; up to +3.00 effective add power

Contact Lens Selection, Fitting and Assessment

A standard maximum plus power to optimal visual acuity subjective refraction was performed. The initial contact lens power was determined using either the vertex corrected spherical equivalent spectacle refraction (Biofinity sphere and Biofinity Multifocal) or using the QuickStart Calculator App from Visioneering Technologies that was available at the time of the study (NaturalVue Multifocal).^{34, 35} To prevent potential unmasking of participants, the contact lenses used in the study were removed from the contact lens packaging by study team members in a secure area inaccessible to study subjects, and study team members inserted all contact lenses.

After a minimum 10 minute settling period, each contact lens was assessed for centration and movement using a Haag‐Streit BQ 900 LED Slit Lamp with Haag‐Streit reticule eyepiece as previously described.³⁴ Lenses with an acceptable fit had a spherical maximum plus to maximum visual acuity over-refraction performed. If a contact lens power change was required, a new contact lenses was inserted by the study staff and another lens settling period was observed. After final contact lens fitting, high- and low-contrast logMAR distance visual acuity under mesopic conditions was measured using the M&S Clinical Trial Suite (M&S Technologies; Niles, IL).³⁴

Straylight Assessment

Mesopic pupil size was measured to the nearest 0.1mm at both study visits with a NeurOptics VIP-300 Pupillometer (NeurOptics, Laguna Hills, CA). Intraocular Straylight measurements were performed on the right eye with the Oculus C-Quant (Oculus, Wetzlar Germany) under mesopic room illumination (<1.0 Lux; Sekonic L-758DR photometer, Tokyo, Japan) with the contralateral eye patched. The C-Quant measures intraocular straylight monocularly using a compensation comparison visual psychophysics approach as described by Franssen et al.³⁶ An annular LED stimulus, with a maximum brightness of 300 cd/m², is presented over a 14 degree test field and represents a straylight source for the eye.³⁷ The central target is divided into right and left hemifields, corresponding to two response buttons located on the base of the unit. Participants were instructed to look at the central fixation target through the device eyepiece and were instructed prior to testing to depress the left or right button corresponding to the side of the stimulus target that flickered more clearly/strongly. Participants were instructed to make their selection as quickly as possible based on their first impression of target flicker while ignoring the surrounding light source. If both sides of the hemifield target ultimately appeared to flicker with equal intensity, they were instructed to make their selection based upon their first impression of the target. Prior to each trial, a demonstration flicker stimulus was displayed to explain the flicker phenomenon.

A run-in training trial measurement with the C-Quant was conducted during Visit 1 prior to collecting straylight outcome data. The training measurement was performed with a crown glass spectacle trial lens without anti-reflective coating. The spectacle trial lens power was the spherical equivalent of the manifest refraction. After the run-in training trial, Straylight measurements of the three contact lens designs were performed in random order over 2 study visits (Figure 1). Straylight measurements with a spherical equivalent spectacle trial lens were made at the start of Visit 2 to avoid any contact lens wear and potential corneal staining prior to testing.

Figure 1.

Sequence of testing for intraocular straylight with the Oculus C-Quant. A run-in training trial measurement with a spherical equivalent trial spectacle lenses was taken at Visit 1 before contact lens fitting, and spectacle lens measures at Visit 2 were performed prior to contact lens fitting. *Lens selection based on study randomization schedule.

The default range setting of “E moderate” was selected for all trials in the study. This setting is the manufacturer’s recommended test range when straylight increases are expected to be mild and no significant pathology is present.³⁸ Reliability metrics were reviewed, including the expected standard deviation value of the individual measuring points (Esd) and the measurement reliability coefficient (Q), with measurements considered acceptable if the subject had an Esd value of < 0.08 and a Q coefficient of > 0.5, in alignment with the manufacturer’s recommendations for a reliable measurement.³⁸

Statistical analysis

Statistical analyses were performed using SPSS Statistics V29 (IBM, Armonk, New York). Straylight data was collected as part of a study examining multifocal contact lens visual performance, and the study sample size calculation was based on detection of change in low-contrast visual acuity between contact lens designs with a sample size of 24 sufficient to detect of a 0.1 LogMAR change at an α of 0.05 with 90% power.³⁴ Statistical analyses for normally distributed data were conducted using paired t-test and repeated-measures analyses of variance (RM-ANOVA) with lens type as the repeated factor. Adjusted post-hoc t-tests were utilized, when appropriate.

To account for inherent straylight levels of enrolled participants, an analysis of straylight residuals was performed using a method similar to that described by Łabuz.³⁰ Because single vision contact lens wear is not associated with an increase in intraocular straylight^{39, 40}, straylight residuals were defined as :

$$\text{Straylight Residual}={\text{Straylight}}_{\text{MFSCL}}-{\text{Straylight}}_{\text{SVCL}}$$

where the straylight measured wearing a single vision contact lens (Biofinity sphere) represents the inherent straylight condition of the eye. Negative straylight residual values represent a decrease in measured straylight wearing a multifocal soft contact lens (Biofinity Multifocal “D” +2.50 add, NaturalVue Multifocal), and positive straylight residual values represent an increase in straylight wearing a multifocal soft contact lens. Straylight residuals between multifocal contact lenses were compared using a paired-samples t-test.

Results

Contact lens fitting, visual acuity and pupil characteristics

Twenty-five participants completed the study. Contact lens fit, visual acuity and pupil characteristics have been previously reported by our group and pertinent findings are summarized in Table 2.³⁴ All participants were determined to have an acceptable contact lens fit. There were no differences in contact lens centration between the Biofinity sphere, Biofinity Multifocal or the NaturalVue Multifocal, with all three contact lenses displaying slight temporal decentration. Multifocal contact lens wear reduced binocular high-contrast logMAR visual acuity by approximately one line under mesopic lighting and mean high-contrast logMAR visual acuity was better than 0.1 logMAR for all designs. Pupil size under the mesopic room lighting conditions used during straylight assessment was not different between the two visits.

Table 2.

Summary of previously published contact lens fit, visual acuity and pupil characteristics from this cohort (Gregory et al.)³⁰

	Biofinity Sphere	Biofinity D MFCL	NaturalVue MFCL	p-value
Contact Lens Decentration, OD (mm, Mean ± SD)*	0.28 ± 0.23	0.28 ± 0.28	0.28 ± 0.21	p = 0.99
High Contrast Binocular Mesopic Visual Acuity (logMAR, Mean ± SD)	−0.05 ± 0.09	0.03 ± 0.09	0.05 ± 0.09	p < 0.001
Low Contrast Binocular Mesopic Visual Acuity (logMAR, Mean ± SD)	0.18 ± 0.096	0.40 ± 0.09	0.42 ± 0.09	p < 0.001
	Visit 1	Visit 2		p-value
Mesopic Pupil Diameter (mm, Mean ± SD)	5.82 ± 0.73 Range: 4.60 to 7.20	5.78 ± 0.62 Range: 5.00 to 7.50		p = 0.68

MFCL = Multifocal Contact Lens

^*Positive values indicate temporal contact lens decentration, negative values indicate nasal decentration.

Intraocular Straylight

Intraocular straylight (mean ± SD) results in Log Straylight units (LogSL) are reported in Figure 2. No difference in LogSL value was found between the spherical equivalent trial spectacle lens training trial at visit 1 (1.16 ± 0.28 LogSL) and the second spherical equivalent trial spectacle lens measurement at visit 2 (1.09 ± 0.17 LogSL; difference 0.07 ± 0.24 LogSL; p = 0.19). When examining LogSL values for the 4 test conditions, LogSL values differed by lens type (RM-ANOVA; p = 0.004). Statistically significant differences in LogSL values were observed between the spherical equivalent trial spectacle lens (1.09 ± 0.17 LogSL) and the Biofinity sphere contact lens (0.97 ± 0.14 LogSL), the Biofinity Multifocal (0.95 ± 0.09 LogSL), and the NaturalVue multifocal (0.93 ± 0.15 LogSL), with the spectacle trial lens displaying greater LogSL values than each contact lens design (all p < 0.05; Tukey’s HSD). No significant differences in LogSL were observed between the three contact lens designs (all p > 0.05; Tukey’s HSD). Straylight residuals for the multifocal contact lenses were −0.02 ± 0.13 LogSL for the Biofinity Multifocal and −0.04 ± 0.15 LogSL for the NaturalVue multifocal. There was no significant difference in straylight residuals between the two multifocal contact lens designs (p = 0.44) (Figure 3).

Figure 2.

Log straylight (LogSL) values for the spectacle trial lens and contact lens designs under mesopic lighting conditions. Error bars represent SD. *p<0.05

Figure 3.

Log straylight residuals (LogSL_MFSCL – LogSL_SVCL) with multifocal contact lens wear. Negative values represent a decrease in straylight. Positive values represent an increase in straylight. Error bars represent SD.

Discussion

Increasing clinical use of multifocal soft contact lenses for slowing myopia progression requires eye care practitioners to understand how these devices affect visual performance in everyday life. When considering visual acuity in non-presbyopic individuals, multifocal contact lenses have been shown to perform well in comparison to spectacle or single vision contact lens correction under high contrast, high illumination conditions; however, multifocal lenses reduce visual acuity and performance under low-contrast or low-illumination conditions.^{18, 19, 34, 41–43}

Although visual acuity with the use of multifocal lenses is well understood^{18, 19, 25, 41}, measurement of visual acuity does not capture the entire experience of patients.^{19, 26} For example, reduction in contrast sensitivity has been found with multifocal contact lenses compared to single vision lenses,^{43, 44} and these objective findings are accompanied by reports of subjective visual quality complaints with multifocal contact lens use.²⁶

In the evaluation of subjective visual complaints, straylight measures have been found to be a reproducible method to quantify function.^{32, 40} An example of this is patients with significant cataracts, where glare and halos are a function of straylight; however, straylight is not responsible for loss of visual acuity.^{27, 45} In healthy individuals, straylight values have been shown to change with increasing age. Guber et al. found that the average straylight measurement for healthy individuals was 1.01 LogSL, with straylight values increasing by an average of 0.10 LogSL per 10 years of age.⁴⁶ In the context of this study, the subjects examined were young, healthy myopes without pathology, and the straylight values observed with contact lens wear and the spectacle trial lens were aligned with these previously reported values for normal individuals.

The effect of contact lens wear on straylight levels has been shown to vary depending on contact lens type and design. Rigid gas permeable (RGP) contact lens use has been found to increase measures of straylight during wear, and straylight values remain slightly increased compared to age-matched normal eyes after RGP removal.⁴⁰ In soft contact lens correction, single vision soft contact lenses have not been found to significantly increase intraocular straylight levels compared to no lens on eye, or when compared to habitual spectacles in highly myopic individuals.^{39, 40} Multifocal soft contact lens effects on straylight is more nuanced. A study of +2.50 diopter add multifocal contact lenses fit on myopic young adults and early presbyopes found a statistically significant increase in straylight with one center-near multifocal design, but no difference with two different center-distance designs and another center-near design with a dilated pupil. Individuals in the study were not fully corrected, with the same distance power (+0.25 diopters) was used for all subjects. The study authors attributed the observed increase in straylight values in the one center-near multifocal design to contact lens material properties, and not to the optical design.³⁰

Pupil size is certainly a significant consideration when considering the visual performance of multifocal contact lenses, and optical modeling suggests that pupil diameter plays a significant role in image quality with center-distance multifocal designs.^{28, 47, 48} In the context of intraocular straylight measurements, the potential for multifocal optics to distort light could impact the test results. It has been reported that multifocal contact lens optics increase light distortion compared to single vision contact lenses with increasing pupil size; however the conclusions of the study were limited due to sample size.²⁹ Another study in presbyopic subjects wearing the Biofinity multifocal lens found that the center-distance design had minimal impact on light distortion in the dominant eye.⁴⁹ In this study, the experimental set up and room lighting were carefully controlled in an attempt to minimize differences in pupil size for each straylight measurement.

When comparing the results of this study with the available literature, the straylight values observed in this cohort suggest that ocular straylight does not contribute to the reduction in visual acuity observed with multifocal contact lenses under low illumination conditions. A reduction in high- and low-contrast logMAR acuity was observed under mesopic conditions with multifocal contact lenses compared to spherical contact lenses; however, the amount of intraocular stray light measured with the C-Quant with both multifocal contact lens types did not differ from that measured with the single vison contact lens. Furthermore, the contact lens straylight values observed in the present study are consistent with those previously reported with single vision contact lenses.^{34, 39, 40} In a study evaluating straylight values between habitual spectacles, spectacle trial lenses and soft contact lenses in young myopes, Gaurisankar et al. did not find any difference in straylight values between the three refractive corrections, while this study found a statistically significant difference in straylight values between the spectacle trial lens and the contact lenses. This difference may be due to the difference in the trial lenses tested in each study. Gaurisankar et al. compared soft contact lenses with the subject’s prescribed spectacles, presumably meniscus lens designs with an anti-reflective coating, and flat design trial lenses provided by the device manufacturer with an anti-reflective coating. In this study, standard spectacle trial lenses of a flat lens design without an anti-reflective coating in 0.25 diopter increments were utilized. This was done to allow comparison between the best corrected spherical equivalent spectacle refraction with the best corrected spherical equivalent contact lens correction, as the manufacturer provided trial lenses come in one diopter increments. The lack of anti-reflective coating on the spectacle trial lenses may explain the difference in straylight observed between spectacle trial lenses and soft contact lenses in this study compared to Gaurisankar et al.³⁹ These results suggest that the observed reduction in mesopic visual acuity with multifocal contact lenses as fit for myopia control is due to the center-distance multifocal contact lens optical profile, and that intraocular stray light scatter does not contribute to visual quality with these lenses.

There are some potential limitations to the study. One such limitation is that pupil size may differ during straylight testing compared to that measured under mesopic lighting conditions. Center-distance aspheric multifocal contact lenses and extended depth of focus designs display a power profile that increases in positive defocus radially from lens center, raising the question of whether pupil size during testing could affect the study results.³⁴ While pupil size and straylight measurements were made under the same room lighting conditions and mesopic pupil size was the same between visits, pupil size is not measured by the C-Quant during straylight testing. The nature of the stimulus used by the C-Quant will produce some pupillary miosis; however, pupil size is unlike to significantly affect our findings as increasing pupil size has been shown to only have a weak effect on straylight measurements in normal eyes.⁵⁰ Additionally, when straylight was examined under dilated pupil conditions for multifocal contact, straylight was only shown to increase with a center-near design but was not found to increase with center-distance designs.^{30, 50} Despite the very different power profiles of the Biofinity D Multifocal and the NaturalVue Multifocal lenses that we studied,³³ no difference in straylight was observed between the two center-distance multifocal designs. Another potential limiting factor of the study is the age of the participant population. The study examined young adult myopes, which were older than individuals typically using contact lenses to slow myopia progression. It is unlikely that the participant age significantly impacts our findings, as straylight values have been shown to remain constant until the age of 45 years,⁵¹ and all study participants were under this age. The final potential limitation of the study is the lack of anti-reflective coating on the spectacle trial lenses used in the study, as previously discussed.

In conclusion, center distance aspheric multifocal and extended depth of focus contact lenses designs did not increase intraocular straylight measures in individuals fit using a myopia control fitting approach. The reported reduction in visual acuity under low illumination conditions with these designs compared to spherical soft contact lens optics cannot be attributed to center-distance multifocal optical profiles increasing intraocular straylight.